A Distributed Antenna System (DAS) is a network of spatially separated antenna nodes that provide wireless service within a geographic area or structure. The spatially separated antenna nodes are coupled to a common node via one or more transport mediums. The common node is also referred to herein as a “host unit”, and can be located at a centralized location. The antenna nodes are located at a location that is remote from the host unit and are also referred to herein as “remote units”.
The host unit is typically communicatively coupled to one or more base stations which allow bidirectional communications between wireless subscriber units within the DAS service area and communication networks such as, but not limited to, cellular phone networks, the public switch telephone network (PSTN), and the Internet. The host unit can be communicatively coupled to the one or more base stations using one or more wired connections (for example, where the base stations are co-located with the host unit) and/or can be communicatively coupled to the one or more base stations using one or more wireless connections (for example, using one or more donor antennas and bi-directional amplifiers).
One type of DAS is referred to as a digital DAS. In a digital DAS, the signals transported between host unit and remote units comprise digital sample streams. A digital sample stream is a stream of digital samples (e.g., I/Q samples) corresponding to an RF bandwidth that was received at the remote unit (in the case of remote unit to host unit transport) or is to be transmitted from the remote unit (in the case of host unit to remote unit transport). To transport a digital sample stream between a host unit and a remote unit, the host unit or remote unit generates a signal that is conditioned for long distance transport over the respective transport medium and modulates the digital sample stream on the signal. The transport medium can comprise optical communication media (for example, optical fiber), copper communication medium (for example, coaxial or CATV cabling and/or twisted-pair cabling), and/or wireless communication links (for example, microwave wireless links). The transport medium can be implemented using various network topologies (for example, point-to-point topologies, star or tree topologies, and ring topologies as well as combinations thereof).
A DAS can be configured to implement simulcast transmission and reception of signals. In the downlink, simulcast refers to the process of transmitting the same signal from multiple remote units. In the uplink, simulcast refers to the process of combining signals from multiple remote units to be received as a single signal. To send the same (i.e., common) signal from multiple remote units, identical digital sample streams are sent to each of the multiple remote units concurrently such that each of the multiple remote units generates and transmits the same signal. To combine signals from multiple remote units, digital sample streams from multiple remote units are combined before being demodulated.
The processes of generating multiple identical digital sample streams for downlink simulcast and combining multiple digital sample streams for uplink simulcast can be performed by a simulcast module. To generate multiple digital sample streams for downlink simulcast, such a simulcast module can receive a digital sample stream from an upstream source (e.g., a host unit), can generate multiple copies of the digital sample stream, and can send each of the copies to a different downstream destination (e.g., a different remote unit) for transmission therefrom. To combine multiple digital sample streams, the simulcast module can receive the multiple digital sample streams, each at the same sample rate and from a different downstream source (e.g., a different remote unit), arithmetically sum corresponding digital samples from each of the digital sample streams to generate a single digital sample stream, and send the single digital sample stream to an upstream destination (e.g., a host unit).
Such a simulcast module can be part of (i.e., integrated in) a host unit and enable the host unit to generate and receive simulcast signals with multiple remote units. A simulcast module can also be part of remote unit and enable multiple remote units to be daisy chained together. A simulcast module can also be part of an intermediate node (also referred to as an “expansion unit” or an “expansion hub”). An intermediate node is located between a host unit and a plurality of remote units and is used to expand the geographical area and/or number or remotes units that a given host unit can service. Such an intermediate node can combine uplink signals from multiple remote units and distribute downlink signals to the multiple remote units.